It is known that modern civil aircraft are controlled by mathematical piloting laws embedded in dedicated digital computers and the inputs of which come from sensors placed on the aircraft and the outputs of which consist of control surface deflection inputs. These control surface deflection inputs are sent to controllers of actuators of these control surfaces.
The entire control chain linking movements of the aircraft and movements of the control surfaces is therefore subject to a time delay depending on the frequency of refreshing the sensors and sampling asynchronisms between the elements of the control chain and the controller of the control surface.
The piloting law is usually computed using a powerful mathematical tool and then transcribed into the computer in the form of gain tables. This method generates multiple steps before the introduction of the gains into the computer and does not enable modification of the objectives of the law in that computer.
Moreover, on a flexible aircraft, the first structural modes of which are situated at frequencies close to those of the piloting modes, it is necessary to apply frequency-domain filtering to the information from the sensors in order to limit aeroservoelastic coupling between the structure of the aircraft and the piloting law.
The mathematical model representing an entire control chain of this kind can be very complex and make the explicit writing of a corresponding piloting law in a computer impossible.